Infectious agent of chickenpox or shingles

Identification of chickenpox or shingles

Clinical features

Varicella (chickenpox)

Chickenpox generally presents with a low-grade fever, malaise and a rash. The rash is firstly maculopapular, then becomes vesicular (blistered) and progresses to crusted lesions over about 5 days. Lesions appear in three or four crops. They are most numerous on the trunk and less so on the face, scalp, limbs and mucous membranes of the mouth. Some cases (about 5 per cent) are subclinical or exceedingly mild in nature.

Adults tend to suffer with more severe disease than children. Rarely, the disease may be fatal.

As vaccination rates have increased, an increasing number of varicella cases now occur among vaccinated persons. Cases of varicella in vaccinated persons (that is, breakthrough cases) are generally much milder, with a lower fever and more rapid recovery. Vaccinated cases often have fewer than 50 rash lesions and fewer vesicles compared with 300 or more lesions and many vesicles in unvaccinated persons.

Newborns and immunosuppressed patients are at greatly increased risk of severe chickenpox.

Herpes zoster (shingles)

VZV remains in a latent state in human nerve tissue and reactivates in about 15–30 per cent of infected persons during their lifetime, resulting in herpes zoster (shingles). Herpes zoster or shingles is characterised by a predominantly unilateral vesicular eruption within a dermatome. It is often associated with severe pain that may precede lesions by 48–72 hours. The rash lasts up to several weeks, depending on severity. The rash is often more widespread and persistent in immunosuppressed patients.

Patients must be carefully evaluated to ensure that there is no eye or auditory nerve involvement when the rash involves the ophthalmic area of the face. Specialist treatment is mandatory in this case, because blindness, hearing impairment or other complications can result.

Incidence increases with age, and children under 12 are rarely affected unless immunosuppressed or initially infected as infants.

Disseminated herpes zoster is a form of shingles characterised by skin lesions outside the affected dermatome, with potential involvement of other organs (for example, causing hepatitis or encephalitis).

A debilitating complication of herpes zoster in many (especially elderly) patients is prolonged pain (post-herpetic neuralgia) that may persist for months after resolution of the skin lesions.

Diagnosis

Confirmation of the diagnosis is generally only required when the clinical picture is atypical. It is made by one of the following:

Incubation period of varicella zoster virus

The incubation period is 2–3 weeks and is usually 14–16 days. This may be prolonged in immunosuppressed persons or following immunoglobulin administration as passive immunisation against varicella.

Public health significance and occurrence of chickenpox or shingles

Chickenpox is a highly contagious but generally mild disease and is endemic in the population. It becomes epidemic among susceptible individuals mainly during winter and early spring. More than 90 per cent of cases are children under 15 years of age.

Herpes zoster (shingles) occurs in 20 per cent of people, mostly when they are elderly due to the reactivation of latent virus from the dorsal root ganglia.

Reservoir of varicella zoster virus

Humans are the reservoir.

Mode of transmission of varicella zoster virus

Chickenpox transmission is mainly person-to-person by airborne respiratory droplets, but also occurs by direct contact with vesicle fluid of chickenpox cases or contact with the vesicle fluid of patients with herpes zoster. Immunosuppressed cases with disseminated herpes zoster may also transmit via respiratory droplets. Indirect contact occurs through articles freshly soiled by discharges from vesicles of infected persons. Scabs are not infective.

Period of communicability of chickenpox or shingles

It is usually communicable for 1–2 days before the onset of the rash, continuing until all the lesions are crusted. Communicability may be prolonged in patients with altered immunity.

People with zoster are considered infectious for a week after lesions appear, when they are moist.

Susceptibility and resistance to chickenpox or shingles

Chickenpox is highly infectious; herpes zoster much less so. More than 80 per cent of nonimmune household contacts of a case of chickenpox will become infected. Nonimmune people exposed to shingles cases will develop chickenpox (not zoster) if they become infected.

Second attacks of chickenpox are rare but do occur.

Infection remains latent in some individuals and can recur years later as shingles.

Patients who are at high risk of severe disease/complications if they do not have immunity include:

infants less than 1 month old

pregnant women

immunosuppressed individuals, including those with haematological malignancies, those on chemotherapy or high-dose steroids, or those with HIV infection.

Control measures for chickenpox or shingles

Preventive measures

In Australia, the varicella vaccine is recommended for nonimmune, healthy individuals from 12 months to 14 years of age. It should be administered at 18 months of age.

It provides protection against infection in 70–90 per cent of individuals. Live attenuated varicella vaccine (VV) is currently available as a monovalent vaccine. Two quadrivalent combination vaccines containing live attenuated measles, mumps, rubella and varicella viruses (MMRV) are also registered in Australia. MMRV is given at 18 months of age.

Nonimmune individuals who should be specifically targeted for vaccination include:

household contacts of immunosuppressed people

healthcare workers

those working with young children, including teachers

women contemplating pregnancy

parents of young children.

Vaccination is contraindicated in immunosuppressed people and pregnant women. For further details, see the current edition of the Australian immunisation handbook (National Health and Medical Research Council).

Immunosuppressed people, pregnant women close to term and newborns should be protected from exposure. If exposure has occurred in these persons, varicella zoster immunoglobulin (VZIG) is effective in modifying or preventing the disease if given within 96 hours of exposure. VZIG is available on a restricted basis through the Australian Red Cross Blood Service.

Control of case

Varicella (chickenpox)

In the nonhospitalised patient with a normal immune system and uncomplicated varicella, aciclovir is not recommended because it provides only marginal benefits. In immunocompromised patients and in normal patients with severe disease or with complications of varicella (such as pneumonitis, hepatitis or encephalitis) aciclovir may be used. Consult the current version of Therapeutic guidelines: antibiotic

General measures include:

tepid bathing or cool compresses, which may help to alleviate itching

exclusion from school until all blisters have dried, or at least for 5 days after eruption first appears. Some remaining dry scabs are not a reason for continued exclusion

advising adults to stay away from work for at least 5 days

avoiding contact with high-risk susceptible persons.

Aspirin should never be given to children under 16 years of age with varicella, because of a strong association with the development of Reye syndrome.

Herpes zoster (shingles)

Some antiviral medications (famciclovir, valaciclovir or aciclovir) have been effective in treating varicella zoster infections in patients with a rash less than 72 hours old. They give pain relief, accelerated healing and may be of benefit in reducing the incidence of postherpetic neuralgia.

More intensive treatment is warranted in high-risk patients. Consultation with an infectious diseases physician is advised. Adequate analgesia should not be forgotten.

Control of contacts

Significant contact is defined as face-to-face contact for at least 5 minutes, being in the same room for greater than 1 hour or household contact.

Varicella vaccination of contacts

Vaccination may be used to prevent or attenuate illness if given to susceptible contacts within 5 days (preferably 72 hours) of first exposure.

Varicella zoster immunoglobulin for contacts

High-risk susceptible contacts where vaccination is not indicated, such as neonates, pregnancy and immunosuppressed persons, should be offered VZIG within 96 hours of exposure. If vaccination is not contraindicated, it should follow at least 5 months later. (See the current edition of the Australian immunisation handbook, National Health and Medical Research Council, for further details and supply.)

Any child with an immune deficiency (for example, leukaemia) or on chemotherapy should be excluded from primary schools or children’s services centres for their own protection. Otherwise, children should not be excluded.

Any nonimmune person admitted to hospital who has a known exposure to varicella should be isolated for days 10–21 after exposure or up to 28 days if given VZIG, to reduce the risk of spread to immunosuppressed patients.

Outbreak measures for chickenpox or shingles

Timely vaccination of susceptible contacts is indicated to contain an outbreak.

Special settings

School

Children with chickenpox are excluded for at least 5 days after the rash appears. A few remaining scabs are not a reason for continued exclusion. Children with shingles (which occurs only rarely) can attend school if the lesions can be covered adequately; however, exclusion from swimming and contact sports should be advised for seven days after the rash appears.

Parents of children with immunosuppressive diseases should be advised of cases of chickenpox in the school because they may wish to voluntarily exclude their own child.

Immunosuppressed and their household contacts

Immunosuppressed people, in particular those with haematological malignancies, are at high risk of more severe infection. VZIG should be offered to these patients if exposed. Susceptible household contacts of these patients should be vaccinated.

Pregnancy

Varicella infection during the first trimester of pregnancy confers a small risk of miscarriage. Maternal infection before 20 weeks rarely may result in the fetal varicella zoster syndrome, with the highest risk (2 per cent) occurring at 13–20 weeks. Clinical manifestations include growth retardation, cutaneous scarring, limb hypoplasia and cortical atrophy of the brain.

Intrauterine infection can also result in herpes zoster in infancy. This occurs in less than 2 per cent of infants. The highest risk is associated with infection in late pregnancy. In the third trimester, maternal varicella may precipitate the onset of premature labour. Severe maternal varicella and pneumonia at any stage of pregnancy can cause fetal death.

Susceptible pregnant women who have been exposed during pregnancy should seek specialist obstetric advice. Susceptibility can be assessed by serological testing for varicella immunoglobin G (IgG). The woman may be offered VZIG and antivirals (famciclovir, valaciclovir or aciclovir), especially where delivery is imminent.

Where chickenpox develops in pregnancy, specialist medical review within 24 hours of rash onset is indicated to consider treatment options.

Newborns

Where newborns develop varicella before 10 days of age, or when maternal chickenpox develops within 7 days of delivery and up to 48-hours postpartum, the neonatal fatality rate is up to 30 per cent without treatment. Treatment of mothers and newborns is vital.

Premature babies and infants less than one month old who develop varicella may require specific treatment. Seek expert advice.

Healthcare workers

On commencement at a new workplace, all healthcare workers with an uncertain history of varicella infection should be serotested and offered immunisation, if they are susceptible.

If a rash develops in the 3 weeks after immunisation, the worker should be removed from contact with other staff patient contact until varicella is excluded or lesions have crusted over.

If a healthcare worker is exposed to a confirmed case of varicella or herpes zoster they may continue working with other staff patient contact, if they have a history of previous infection or immunisation. They should be advised to report any febrile symptoms or rash developing within 3 weeks of exposure and then avoid contact with other staff patient contact until varicella is confidently excluded.

If the worker is susceptible and has been exposed, vaccination within 5 days of exposure is indicated. They should report any rash that occurs within 6 weeks of vaccination and avoid patient contact, as above. If vaccination is refused, no patient contact should take place between days 10 and 21 after first exposure.

Shingles in a healthcare worker

Workers should not care for high-risk patients until lesions have crusted over. Other patients can be cared for as long as lesions can be adequately covered.

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